sql - 使用 Rails 在 Postgres 中开发自定义函数

Question

假设我有一个大型复合公式来计算小部件的质量

quality = 0.4(factory_quality) + 0.3(1/days_since_manufacture) + 0.3(materials_quality)

这三个因素中的每一个本身都是函数，它们需要连接到工厂表，并且可能需要连接到带有 Material 的 Material list 连接表，其中关联的记录是平均的或其他的。

在架构上，您将如何在 Rails 项目中管理它？ a) 生成正确的查询和 b) 在 Rails 中管理代码的最佳实践是什么？

目前对于 sql，我在 FROM 语句中使用子查询:

SELECT *,
  (0.4 * factory_quality + 0.3 * (1/days_since_manufacture) + 0.3 * materials_quality) AS quality
FROM (
  SELECT *,
    ((factories.last_inspection_score + factories.variance_score)/2) AS factory_quality,
    (now() - widgets.created_at) AS days_since_manufacture,
    SUM(materials.quality_score) AS materials_quality
  FROM widgets,
  JOIN factories ON widget.factory_id = factories.id
  JOIN bills_of_materials ON widget.id = bills_of_materials.widget_id
  JOIN materials ON bills_of_materials.material_id = materials.id
  GROUP BY widgets.id
) AS widgets;

在 Rails 中，我主要使用 ActiveRecord 来实现:

class Widget < ActiveRecord::Base
  belongs_to :factory
  has_many :bills_of_material
  has_many :materials, through :bills_of_material

  class << self
    def with_quality
      select([
        "widgets.*",
        "(0.4 * factory_quality + 0.3 * (1/days_since_manufacture) + 0.3 * materials_quality) AS quality"
      ].join(",")
      .from("(#{subquery}) AS widgets")
    end
    private
      def subquery
        select([
          "widgets.*",
          "((factories.last_inspection_score + factories.variance_score)/2) AS factory_quality",
          "(now() - widgets.created_at) AS days_since_manufacture",
          "SUM(materials.quality_score) AS materials_quality"
        ].join(","))
        .joins(:factory,:materials)
        .group("widgets.id")
        .to_sql
      end
  end
end

也就是说，我觉得我可以在 Postgres 中将其设为自定义函数，将所有这些 sql 移到该函数中，迁移它，然后清理 rails 使其看起来像

def with_scores
  select("*,quality_score_func(id) AS quality")
end

或类似的东西，但我觉得通过数据库迁移来管理不断发展的公式会很痛苦，更不用说找出公式的当前形式的任务了是(而且也很难测试)。

其他人是如何解决这个问题的？有什么提示或建议吗？

Answer 1

这是我能想到的最不使用 SQL 的方法。我无法真正对此进行测试，但希望它至少是一个有用的练习。据我了解，如果您使用 includes，Rails 会将连接放在一起并在一个查询中预先加载所有相关数据。

# All of these are additional Widget instance methods; you decide if they are private
#
# Example use:
#
#   @widget = Widget.includes(:factory, :materials).find(1)
#   puts @widget.quality_score
# or
#   @widgets = Widget.includes(:factory, :materials).all
#   @widgets.each { |widget| puts widget.quality_score }

# Consider making these weights named constants
def quality_score
  0.4 * factory_quality + \
  0.3 * (1/days_since_manufacture) + \
  0.3 * (materials_quality_score )
end

def days_since_manufacture
  Time.now - created_at
end

def factory_quality
  (factory.last_inspection_score + factory.variance_score)/2
end

def materials_quality_score
  materials.inject(0) {|sum, material| sum + material.quality_score }
end